Triple response
Chapter: 2
Also known as the wheal and flare reaction. When the skin is stroked with a blunt object, a dull red line develops almost immediately. This is followed soon by an enlarging red halo (the flare) and elevation of the skin (swelling; the wheal) along the original red line. The original red line is the result of immediate, transient vasodilatation (hyperemia, mainly of precapillary arterioles). The spreading flare is the result of spreading vasodilatation, while the wheal is produced by loss of fluid and plasma proteins from the transiently permeable postcapillary venules (edema).